Elsevier

Biological Psychiatry

Volume 78, Issue 7, 1 October 2015, Pages 441-451
Biological Psychiatry

Archival Report
Gq-DREADD Selectively Initiates Glial Glutamate Release and Inhibits Cue-induced Cocaine Seeking

https://doi.org/10.1016/j.biopsych.2015.02.016Get rights and content

Abstract

Background

Glial cells of the central nervous system directly influence neuronal activity by releasing neuroactive small molecules, including glutamate. Long-lasting cocaine-induced reductions in extracellular glutamate in the nucleus accumbens core (NAcore) affect synaptic plasticity responsible for relapse vulnerability.

Methods

We transduced NAcore astrocytes with an adeno-associated virus vector expressing hM3D designer receptor exclusively activated by a designer drug (DREADD) under control of the glial fibrillary acidic protein promoter in 62 male Sprague Dawley rats, 4 dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor mice, and 4 wild-type littermates. Using glutamate biosensors, we measured NAcore glutamate levels following intracranial or systemic administration of clozapine N-oxide (CNO) and tested the ability of systemic CNO to inhibit reinstated cocaine or sucrose seeking following self-administration and extinction training.

Results

Administration of CNO in glial fibrillary acidic protein-hM3D-DREADD transfected animals increased NAcore extracellular glutamate levels in vivo. The glial origin of released glutamate was validated by an absence of CNO-mediated release in mice expressing a dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor variant in glia. Also, CNO-mediated release was relatively insensitive to N-type calcium channel blockade. Systemic administration of CNO inhibited cue-induced reinstatement of cocaine seeking in rats extinguished from cocaine but not sucrose self-administration. The capacity to inhibit reinstated cocaine seeking was prevented by systemic administration of the group II metabotropic glutamate receptor antagonist LY341495.

Conclusions

DREADD-mediated glutamate gliotransmission inhibited cue-induced reinstatement of cocaine seeking by stimulating release-regulating group II metabotropic glutamate receptor autoreceptors to inhibit cue-induced synaptic glutamate spillover.

Section snippets

Animal Housing and Surgery

All procedures were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Association for the Assessment and Accreditation of Laboratory Animal Care International. Male Sprague Dawley rats (250 g to 300 g on arrival; Charles River Laboratories, Wilmington, Massachusetts) were individually housed in a temperature- and humidity-controlled environment with a 12-hour dark/light cycle. Experiments were conducted during the animals׳

Astrocyte-Specific Expression of Gq-DREADD

Injection of the GFAP-Gq-DREADD virus in the NAcore produced fields of transduced astrocytes, easily distinguished from neurons given their morphology and lack of co-localization with a NeuN neuronal marker (Figure 1A,B). The GFAP-Gq-DREADD virus produced an immunoreactivity pattern consistent with astrocyte labeling (30, 31, 32), and astrocyte-specific expression of Gq-DREADD was very likely given the apparent co-localization of the astrocyte-specific filament protein GFAP and viral HA signals

Discussion

Our data demonstrate that Gq-DREADD-mediated enhancement of NAcore glial-glutamate release was SNARE-dependent and that the inhibitory effect of glial-glutamate on reinstated cocaine seeking was mediated by mGluR2/3. Several groups have shown that activation of Gq-DREADD elevates [Ca2+]i, potentially leading to enhanced gliotransmission (21, 34). Here, we show that activating Gq-DREADD in NAcore astrocytes promotes the release of glutamate. In support, hippocampal studies reveal a parallel

Acknowledgments and Disclosures

This research was supported by Grants from the National Institutes of Health to PWK (R015369 and DA003906). MDS was also partially supported by a National Institute on Drug Abuse Training Grant (T32 DA 7288-22).

The authors report no biomedical financial interests or potential conflicts of interest.

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